1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having fibers protruding from pulley engaging side surfaces thereon.
2. Background Art
When conventional power transmission belts are initially installed on a pulley system, the belts are highly tensioned. The belts are thus pressed tightly against cooperating pulleys. The belt rubber tends to stick to the pulley surfaces which accounts for positive force transmission. However, the high frictional force between the belts and pulleys also accounts for the generation of unwanted noise.
It is known to embed short fibers in the V-shaped portion of a power transmission belt. The fibers are oriented in a lateral direction to enhance lateral pressure resistance on that part of the belt which contacts a cooperating pulley. These fibers are commonly exposed at the laterally oppositely facing pulley engaging side surfaces so as to improve wear resistance at the side surfaces of the belt.
It is also known to embed short fibers in a power transmission belt and to have the fibers protrude from the pulley engaging side surfaces on at least that portion of the belt that frictionally engages a cooperating pulley. Protruding fibers reduce wear on the belt side surfaces and also prevent sticking between the belt side surfaces and a cooperating pulley to alleviate the aforementioned noise generation problem.
It is also known to use short aramid fibers in that portion of the belt that is engaged by a cooperating pulley. Aramid fibers exhibit excellent wear resistance. In Japanese Patent Laid-Open No. 1-164839, aramid fibers are shown protruding from the pulley engaging side surfaces on a power transmission belt to improve the durability thereof.
When a belt with protruding aramid fibers is operated, the cooperating pulleys cause the protruding portions of the aramid fibers to be bent against the side surfaces of the belt. The bent fibers then cover a significant portion of, if not the entire, side portion of the belt which engages the cooperating pulleys in operation. The aramid fibers protect the pulley engaging side surfaces of the belt from wear.
In operation, the pulleys not only bend the exposed portions of the aramid fibers but eventually embed the fibers into the rubber of the side surfaces. This embedding is advantageous in terms of wear resistance in that the fibers remain intact for a long period of time. However, in certain systems, this condition is undesirable.
More particularly, in systems that utilize an automatic tensioner to maintain a predetermined tension on a belt, if the belt does not slip at the time of the initial set-up, it normally will not slip thereafter. That is because the tensioner maintains a relatively constant tension on the belt throughout its life.
However, in a system in which belts are pre-tensioned by relatively moving one or more pulleys, and no tensioner is used, a problem arises. Over the life of the belt, the tension may be reduced as the belt stretches or one or more of the pulleys repositions. The aramid fibers exposed at the pulley engaging side surfaces reduce the friction between the slackened belt and the cooperating pulley so that the belt may slip on the pulley. This reduces the power transmitting capability of the belt.
Accordingly, while the use of laterally extending and protruding aramid fibers has significant advantages, conventional type belts having aramid fibers do have a problem by reason of the embedding of the fibers. Since the power transmission belt is designed to positively transmit power, any slippage of the belt presents a serious problem.